The present invention pertains generally to a system and method for manufacturing components for implantable medical devices such as batteries or capacitors.
Devices for heat sealing thermoplastics are generally known. Examples of heat sealing apparatus are disclosed in the patents described below.
U.S. Pat. No. 4,268,338 to Peterson shows a pressure die 17, preferably of Delrin, having a profiled face 17a that provides a greater amount of pressure at the outer edge 17b of the die. In that manner, the outer edge 17b of the pressure die sinks into the thermoplastic material sheets P1, P2 a distance sufficient to form a parting line while the remaining profiled face 17a applies pressure sufficient to achieve a weld between the two layers of thermoplastic material.
U.S. Pat. No. 5,028,294 to England relates to a for heat welding a plastic motif to a textile base and comprising a welding ledge 12b and a cutting edge 14, best shown in FIG. 5.
U.S. Pat. No. 3,577,820 to Silverstein pertains to a die for sealing or cutting thermoplastic material. Heated die 45 is machined from ribbon or bar stock of a material such as nichrome and inlaid in a groove 30 formed in a rigid plate 20 of insulated material. FIGS. 13 and 14 illustrate dies having a longitudinally extended rib 48 in the form of a raised portion.
U.S. Pat. No. 4,055,456 to Carnegie, Jr. pertains to an impulse heat-sealing machine having an etched metal foil heater element 127 having a TEFLON(copyright) non-stick layer provided thereon. The heater element serves to seal two thermoplastic sheets together at a seam while a proximate knife blade 122 severs the joined sheets from the stock material.
U.S. Pat. No. 3,614,383 to Watts, Jr. pertains to an apparatus for cutting and/or sealing plastic film, and includes an impulse-heated cutting device and a pressure pad provided on opposite sides of the film. The cutting device includes a support frame member and a resistance-heated element formed by a corrugated ribbon supported in the frame by a dielectric material. An edge of the resistance ribbon projects from the support frame towards a pressure pad 73 for cutting and/or sealing a film sheet when the film is compressed between the pressure pad and the resistance element.
The problem with the prior art is that while it describes various heat sealing apparatus, the material to be heat sealed is not precisely cut to form. This can lead to waste with sealed envelopes of too little or too much material being used. In the former case, the envelope can be easily compromised, while the latter situation can lead to an improper fit as the excess material takes up space intended for other components. This is especially the case in electrochemical cells.
What is needed is a system, for precisely cutting and sealing separator materials around electrode assemblies, that is reliable, economical and user friendly.
The present invention meets the above-described need by providing a system and method for cutting and heat sealing polypropylene film and/or other separator material around individually shaped cathode, anode or other active components, for use in a battery or capacitor and/or other implantable medical device.
The system includes a laser material cutting and perforating mechanism and a thermo-sealing apparatus.
The laser cutting and perforating system provides for cutting guide holes and other openings in the separator with a high degree of accuracy. The guide holes in the separator are used to position the separator in the thermo-sealing apparatus for sealing.
The thermo-sealing apparatus includes a fixture base that provides a mounting surface for a dielectric platform, acts as a heat sink, and provides a mounting surface for the necessary electrical connections.
The dielectric platform acts as a precision track for retaining a heating element during repeated heating and cooling cycles. The dielectric platform also acts as an insulator during the sealing process.
The track on the dielectric platform receives a heating element. The heating element is the portion of the fixture that does the actual cutting and sealing of the film. The geometry of the element is important to the process. The element is machined in two thicknesses. The raised or thicker portion provides the precise cutting dimension while the lower or thinner area provides a precision seal width. The element is chemically or mechanically machined on a thin metallic plate. The element design is unique to each individual sealing operation in size and shape.
The lower platen of the thermo-sealing apparatus includes the dielectric material and the heating element. The dielectric material has a pair of openings for a set of retractable pins that provide for precise positioning of the cathode or anode assembly being sealed. The pins are retractable such that the assemblies can be removed from the device after sealing without damaging the assembly. Also, the pins can be retracted for storage. The lower platen also includes a set of locating pins for positioning the separator material.
The upper platen includes a vulcanized, molded silicone rubber pad. The silicone rubber acts as a pressure pad for sealing.
Both the upper and lower platens are covered with a pressure-sensitive adhesive tape to provide an insulating layer between the heating element and the rubber pad.